(a) Technical Field of the Invention
The present invention generally relates to backlight modules, and more particularly to a backlight module using light guiding devices in its lamp reflector to compensate insufficient lighting in the corner areas of its light guide plate.
(b) Description of the Prior Art
A typical liquid crystal display (LCD) device usually adopts a planar light source provided by a backlight module.
As illustrated in FIG. 1, the backlight module 1 is mainly composed of a light guide plate 11, a reflection plate 12, a number of diffusion films 13 and prism sheets 14, and a lamp 15. The light guide plate 111 has a light exiting side 111, a reflection side 112 opposite to the light exiting side 111, and at least a light entering side 113 at the flank. The reflection plate 12 is attached to the reflection side 112 of the light guide plate 11, and the surface of the reflection side 112 is densely dispersed with light guiding dots 114. The diffusion films 13 and prism sheets 14, on the other hand, are attached to the light exiting side 111 of the light guide plate 11. The cold cathode fluorescent lamp (CCFL) 15 is arranged along the light entering side 113 and is wrapped almost completely inside a lamp reflector 16.
As shown in FIG. 2, lights emitted from the lamp 15 enters directly, or after being reflected by the lamp reflector 16, into the light guide plate 11 via its light entering side 113. The lights are then guided by the refraction and reflection effects of the light guiding dots 114 and the reflection plate 12 to emit from the light guide plate 11 via its light exiting side 111. The lights are then Further evenly distributed and focused by the diffusion films 13 and the prism sheets 14, so as to achieve a uniform planar backlight.
To enhance the LCD's lighting efficiency, quite a few designs have already been disclosed in the past regarding, for example, the form factor of the light guide plate 11, the shape and distribution of the light guiding dots 114, etc. There are also teachings about the design of the lamp 15 and the lamp reflector 16 that can be applied to various types of backlight modules.
According to the foregoing description, the lamp 15 is the only self-luminous device in the backlight module 1. At the two ends of the lamp 15's tubular body 151 are the electrodes 152 for the conduction of electricity. The electrodes 152 themselves do not emit lights and the lights emitted from the tubular body 151 are also weaker towards the two electrodes 152, as illustrated in FIG. 3.
As also shown in FIG. 4, when there are two opposite lamps 15 arranged at two light entering sides 113, due to the non-uniform distribution of luminance along the lamps 15's tubular bodies 151, there are dim areas 115 at the four corners of the light guide plate 11, which reduces the usability of the backlight module 1 significantly.
Such an undesirable effect would become even more disturbing as the dimension of the backlight module is increased for use in a large-scale display. The dim corner areas of the light guide plate in effect reduce the viewing region of the display significantly.